The directory 'PolyVoxCore' is appearing twice in the PolyVox include path as described here: http://www.volumesoffun.com/phpBB3/viewtopic.php?f=15&t=543
Now, in the source distribution we have unusual paths by design (i.e. library/PolyVoxCore/include/PolyVoxCore/). This is done so that code can compile against the installed version in Windows (where we have a path like 'Program Files/PolyVoxCore/include') and on Linux (where we have a path like /usr/include/PolyVoxCore) as well as against the source distribution.
But I don't think this unusual file layout was supposed to spill into the installed version of the library? At least, it's worth checking this before the next release.